Failure analysis on tee pipe of duplex stainless in an oilfield

Abstract

During the hydraulic test in the station of an oil field, a tee-pipe of S32205 duplex stainless burst into several fragments without reaching the target pressure. In order to clarify the failure cause, visual inspection, chemical composition, mechanical test, hardness test, Charpy impact test, heat treatment, and finite element analysis were carried out in this paper. The results show the chemical composition of tee meets the requirements of the standard for S32205 duplex stainless steel, and the tensile property, hardness, Charpy impact and content of harmful phase do not meet the requirements of reference standard. The presence of sigma phase in the tee which induced by the improper heat treatment after cold forming makes the material hard and brittle. In the case of micro defects, the pressure bearing capacity of tee joint will be reduced, resulting in brittle cracking. Therefore, the quality control of tee should be strengthened, the heat treatment should be implemented strictly and nondestructive inspection of tee can be carried out such as field micro-hardness test and metallographic examination. Considering the burst failure case of tee pipe was rarely reported so far, the findings of this paper would provide useful quality control advice in the future.